Zeolites are materials composed by silicum oxide and oxides of other elements commonly aluminum, that are characterized by their high specific surface areas, high microporosity (pores <2 nm) and capacity to undergo cation exchange; moreover, they present structures that are composed by TO4 (T=Si or Al) tetrahedra that ensemble together to form chains and rings that finally generate tridimensional structures conforming intracrystallines spaces and pores and produce voids and channels at the molecular dimension, commonly in the order of 0.4 to 12 nm. Different possible arrays generate a great number of tridimensional structures possessing individual characteristics
Zeolites have a variety of applications such as catalysts and adsorbents. They are materials found in nature, but those prepared synthetically have a higher number of commercial applications.
Zeolites containing silica and aluminum are the most common. The presence of aluminum with tetrahedral coordination generates an excess of negative charge in the structure, which is neutralized by the presence of cations (called compensation cations) commonly alkyl or alkyl earth cations, which are interchangeable.
Among the zeolites with higher commercial interest, Faujasite Y-type structures stress out. These zeolites present a cubic crystalline structure identified by solids X Rays Diffraction (Joint Committee on Powder Diffraction Standards, JCPDS Card 12 0246). They characterize for presenting a pore size 0.74 nm tridimensional system, with specific area values above 700 m2/g (Langmuir method), determined by means of 77 K Nitrogen adsorption.
The Faujasite Y-type zeolites are mainly used as base material for catalysts for the FCC process (Fluid Catalytic Cracking) of interest to the oil refining industry, whereby crude oil heavy fractions are converted into lighter fractions of high commercial value (gasoline and LP gas, for example). The FCC process is characterized by operating at high temperature conditions (up to 750° C. in the stage of catalyst regeneration) in the presence of water steam and metals under drastic thermal changes, thus requiring the zeolite to have acidic properties and stability under such conditions.
The way Faujasite Y-type zeolites are synthesized at present produces materials that are not suitable as catalysts and consequently, they have to be modified; one of the first modifications to be performed is to eliminate sodium in order to provide acid properties.
Though well dominated in the state of art, the different treatments for modifying the Faujasite Y-type zeolites to be used as catalysts in the FCC process include successive washing stages with ammonia solutions and thermal treatment at high temperatures.
Similarly, the dealumination of the zeolite structure with the aim of increasing zeolite stability is carried out by means of thermal, hydrothermal and controlled chemical treatments, generally conducted in several stages. Besides aluminum extraction, these treatments frequently produce partial destruction of the crystalline structure thus reducing the intracrystalline zeolite area, producing amorphous materials and an increase of the material average pore size towards the mesoporous region. It is frequently important to be able to control meso-porosity of the FCC catalyst, as this enhances molecule conversion from higher size hydrocarbons contained in the oil heavy fractions. This is collaterally produced in the stabilization treatments but also takes place through the incorporation of other materials, not related to the catalyst structure, frequently alumina or amorphous alumino-silicates.
Consequently, since zeolite modification treatments mean successive operations resulting into high manufacturing costs, their simplification is highly desirable.
Because of the above, there is a great interest for finding more efficient and economical processes and/or methods for obtaining zeolites with more suitable properties for use as catalysts.
U.S. Pat. No. 6,054,113 (A), issued on Apr. 25, 2000, discloses a method to prepare Faujasite Y-type zeolites with high silica content through a cationic interchange treatment with ammonia and mineral acid ions and a water steam calcination treatment.
Also, U.S. Pat. No. 5,601,798 (A), issued on Feb. 11, 1997, discloses a process to prepare a Y-type zeolite with a 2 to 60 nm mesoporous volume from combining hydrothermal and chemical treatments.
U.S. Patent Publication No. 2008/014140 (A1), published on Jan. 17, 2008, discloses a manufacturing method for zeolites showing different porous systems, by means of the decomposition by calcination or combustion of carbohydrates such as sucrose previously soaked in zeolites.
U.S. Patent Publication No. 2007/0227351 (A1), published on Oct. 4, 2007, discloses the synthesis of meso-structured zeolites from a preformed zeolite, treated in a media using ammonia salts or alkyl ammonia, mineral acids such as fluorohydric acid and surfactants followed by hydrothermal treatments in autoclave.
The former technologies, known by the applicant, were improved by means of the process of the present invention, as it produces in one stage a modified Faujasite Y-type Zeolite and a mesoporous material associated to the Faujasite Y-type Zeolite, where the sodium content of the modified Faujasite Y-type zeolite is lower with respect to that in the pristine Faujasite Y-type Zeolite.
Therefore, one of the aims of the present invention is to supply a process for modifying the physical and chemical properties of Faujasite Y-type Zeolites, carrying out in one stage and jointly the sodium content modification and producing a meso-porous material that modifies the Langmuir total specific area, the micro-pore area, the pore volume and the pore size distribution of the pristine Faujasite Y-type Zeolite.
An additional purpose of the present invention is to supply a process to produce a modified Faujasite Y-type Zeolite, with a sodium content up to a 75% lower than that of the pristine Faujasite Y-type Zeolite and a mesoporous material, associated to the modified Faujasite Y-type Zeolite, presenting a pore average size from 2 to 100 nm.
One more purpose for the present invention is to supply a process for producing materials presenting a bimodal or polymodal pore distribution, and where the modified Faujasite Y-type Zeolite proportion, regarding the mesoporous material associated to the modified Faujasite Y-type Zeolite, can be regulated through the process operation conditions.